Semiconductor Device with Multi-Layer Dielectric and Methods of Forming the Same

ABSTRACT

Semiconductor device and the manufacturing method thereof are disclosed herein. An exemplary semiconductor device comprises a fin disposed over a substrate, a gate structure disposed over a channel region of the fin, such that the gate structure traverses source/drain regions of the fin, a device-level interlayer dielectric (ILD) layer of a multi-layer interconnect structure disposed over the substrate, wherein the device-level ILD layer includes a first dielectric layer, a second dielectric layer disposed over the first dielectric layer, and a third dielectric layer disposed over the second dielectric layer, wherein a material of the third dielectric layer is different than a material of the second dielectric layer and a material of the first dielectric layer. The semiconductor device further comprises a gate contact to the gate structure disposed in the device-level ILD layer and a source/drain contact to the source/drain regions disposed in the device-level ILD layer.

This is a divisional application of U.S. patent application Ser. No.16/597,205, filed Oct. 9, 2019, which is a non-provisional applicationof and claims benefit of U.S. Provisional Patent Application Ser. No.62/771,626, filed Nov. 27, 2018, the entire disclosures of which areincorporated herein by reference. This application is related to andalso claims priority to U.S. patent application Ser. No. 17/871,272,filed Jul. 22, 2022, which is a divisional application of U.S. patentapplication Ser. No. 16/597,205, filed Oct. 9, 2019, the entiredisclosures of which are incorporated herein by reference.

BACKGROUND

The electronics industry has experienced an ever-increasing demand forsmaller and faster electronic devices which are simultaneously able tosupport a greater number of increasingly complex and sophisticatedfunctions. These goals have been achieved by scaling down semiconductorIC dimensions (e.g., minimum feature size) and thereby improvingproduction efficiency and lowering associated costs. However, suchscaling has also introduced increased complexity to the semiconductormanufacturing process. Multi-gate devices have been introduced toimprove gate control, reduce OFF-state current, and reduce short-channeleffects (SCEs). Multi-gate devices are compatible with conventionalcomplementary metal-oxide-semiconductor (CMOS) processes and theirthree-dimensional structure allows them to be aggressively scaled whilemaintaining gate control and mitigating SCEs. However, aggressivescaling down of IC dimensions has resulted in decreased distance betweencontacts. When the mask slots are too close to meet the resolutionlimit, metal contact bridge may be formed and cause poor deviceperformance. In addition, single layer interlayer dielectric (ILD) maycause small contact to contact TDDB window and shorten the device life.Thus, existing techniques have not proved entirely satisfactory in allrespects.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure is best understood from the following detaileddescription when read with the accompanying figures. It is emphasizedthat, in accordance with the standard practice in the industry, variousfeatures are not drawn to scale and are used for illustration purposesonly. In fact, the dimensions of the various features may be arbitrarilyincreased or reduced for clarity of discussion.

FIG. 1 illustrates a flowchart of an example method for making asemiconductor device in accordance with some embodiments of the presentdisclosure;

FIG. 2 illustrates a three-dimensional perspective view of an examplesemiconductor device in accordance with some embodiments of the presentdisclosure;

FIGS. 3A-14A illustrate planar top views of the example semiconductordevice at intermediate stages of the method of FIG. 1 in accordance withsome embodiments of the present disclosure;

FIGS. 3B-14B illustrate cross-sectional views along plane B-B′ shown inFIGS. 3A-14A of the example semiconductor device at intermediate stagesof the method of FIG. 1 in accordance with some embodiments of thepresent disclosure;

FIGS. 3C-14C illustrate cross-sectional views along plane C-C′ shown inFIGS. 3A-14A of the example semiconductor device at intermediate stagesof the method of FIG. 1 in accordance with some embodiments of thepresent disclosure;

FIGS. 3D-14D illustrate cross-sectional views along plane D-D′ shown inFIGS. 3A-14A of the example semiconductor device at intermediate stagesof the method of FIG. 1 in accordance with some embodiments of thepresent disclosure;

FIGS. 15A-15P illustrate void positions and dimensions of the examplesemiconductor device; and

FIG. 16 illustrates the positions and dimensions of voids at a highermagnification.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, orexamples, for implementing different features of the invention. Specificexamples of components and arrangements are described below to simplifythe present disclosure. These are, of course, merely examples and arenot intended to be limiting. For example, the formation of a firstfeature over or on a second feature in the description that follows mayinclude embodiments in which the first and second features are formed indirect contact, and may also include embodiments in which additionalfeatures may be formed between the first and second features, such thatthe first and second features may not be in direct contact.

In addition, the present disclosure may repeat reference numerals and/orletters in the various examples. This repetition is for the purpose ofsimplicity and clarity and does not in itself dictate a relationshipbetween the various embodiments and/or configurations discussed.Moreover, the formation of a feature on, connected to, and/or coupled toanother feature in the present disclosure that follows may includeembodiments in which the features are formed in direct contact, and mayalso include embodiments in which additional features may be formedinterposing the features, such that the features may not be in directcontact. In addition, spatially relative terms, for example, “lower,”“upper,” “horizontal,” “vertical,” “above,” “over,” “below,” “beneath,”“up,” “down,” “top,” “bottom,” etc. as well as derivatives thereof(e.g., “horizontally,” “downwardly,” “upwardly,” etc.) are used for easeof the present disclosure of one features relationship to anotherfeature. The spatially relative terms are intended to cover differentorientations of the device including the features. Still further, when anumber or a range of numbers is described with “about,” “approximate,”and the like, the term is intended to encompass numbers that are withina reasonable range including the number described, such as within +/−10%of the number described or other values as understood by person skilledin the art. For example, the term “about 5 nm” encompasses the dimensionrange from 4.5 nm to 5.5 nm.

The present disclosure is generally related to semiconductor devices andthe fabrication thereof, and more particularly to methods of fabricatingfield-effect transistors (FETs), such as multi-gate devices.

One such multi-gate device that has been introduced is the finfield-effect transistor (FinFET). The FinFET gets its name from thefin-like structure which extends from a substrate on which it is formed,and which is used to form the FET channel. In a FinFET device, a channelregion of a single device may include multiple layers of semiconductormaterial of physically separated from one another, and a gate of thedevice is disposed above, alongside, and even between the semiconductorlayers of the device. This configuration is called gate-all-around (GAA)devices, which allow more aggressive gate length scaling for bothperformance and density improvement. The present disclosure is generallyrelated to formation of multi-gate devices, including FinFETs and GAAdevices, wherein a three-layer interlayer dielectric (ILD) feature isformed to provide selectivity when forming gate contact or source/drain(S/D) contact to avoid the metal bridge issue. In addition, the threelayers structure of the three-layer ILD feature can provides bettercontact to contact time-dependent dielectric breakdown (TDDB) window soas to extend the device life. Of course, these advantages are merelyexemplary, and no particular advantage is required for any particularembodiment.

FIG. 1 illustrates a flow chart of a method 100 for forming asemiconductor device 200 (hereafter called device 200) in accordancewith some embodiments of the present disclosure. Method 100 is merely anexample and is not intended to limit the present disclosure beyond whatis explicitly recited in the claims. Additional operations can beperformed before, during, and after method 100, and some operationsdescribed can be replaced, eliminated, or moved around for additionalembodiments of the method. Method 100 is described below in conjunctionwith other figures, which illustrate various three-dimensional, planartop views, and cross-sectional views of device 200 during intermediatesteps of method 100. In particular, FIG. 2 illustrates athree-dimensional view of device 200. FIGS. 3A-14A illustrate planar topviews of device 200 at intermediate stages of the method of FIG. 1 inaccordance with some embodiments of the present disclosure. FIGS. 3B-14Billustrate cross-sectional views of device 200 taken along plane B-B′ inFIGS. 3A-14A (that is, along an x-direction); FIGS. 3C-14C illustratecross-sectional views of device 200 taken along plane C-C′ in FIGS.3A-14A (that is, along an x-direction), and FIGS. 3D-14D illustratecross-sectional views of device 200 taken along plane D-D′ in FIGS.3A-14A (that is, along a y-direction).

Device 200 may be an intermediate device fabricated during processing ofan integrated circuit (IC), or a portion thereof, that may includestatic random-access memory (SRAM) and/or other logic circuits, passivecomponents such as resistors, capacitors, and inductors, and activecomponents such as p-type FETs (PFETs), n-type FETs (NFETs), fin-likeFETs (FinFETs), metal-oxide semiconductor field effect transistors(MOSFET), complementary metal-oxide semiconductor (CMOS) transistors,bipolar transistors, high voltage transistors, high frequencytransistors, and/or other memory cells. Device 200 can be a portion of acore region (often referred to as a logic region), a memory region (suchas a static random access memory (SRAM) region), an analog region, aperipheral region (often referred to as an input/output (I/O) region), adummy region, other suitable region, or combinations thereof, of an IC.In some embodiments, device 200 may be a portion of an IC chip, a systemon chip (SoC), or portion thereof. The present disclosure is not limitedto any particular number of devices or device regions, or to anyparticular device configurations. For example, though device 200 asillustrated is a three-dimensional FET device (e.g., a FinFET), thepresent disclosure may also provide embodiments for fabricating planarFET devices. FIGS. 2, 3A-14A, 3B-14B, 3C-14C, 3D-14D, 15A-15P, and 16have been simplified for the sake of clarity to better understand theinventive concepts of the present disclosure. Additional features can beadded in device 200, and some of the features described below can bereplaced, modified, or eliminated in other embodiments of device 200.

Referring to FIGS. 1 and 2 , at operation 102, method 100 providesdevice 200, which includes one or more fins 206 protruding from asubstrate 202 and separated by an isolation structure 204, and one ormore gate structures 210 disposed over substrate 202 and fins 206. Gatestructures 210 define a channel region, a source region and a drainregion of fins 206. Gate structures 210 may include gate electrodes 212and gate spacers 214 disposed on sidewalls of gate electrodes 212. Gatestructures 210 may include other components such as one or more gatedielectric layers 216 disposed over isolation structure 204 andsubstrate 202 and below electrodes 212, a barrier layers, a glue layer,a capping layer, other suitable layers, or combinations thereof. Variousgate hard mask layers 220 are disposed over gate electrode layer 212 andmay be considered a part of the gate structures 210. Device 200 alsoincludes S/D features 250 epitaxially grown over S/D regions of fins206. It is understood components included in device 200 are not limitedto the numbers and configurations as shown in FIG. 2 . More or lesscomponents, for example, more fins and gate structures, may be includedin device 200, as shown in FIGS. 3A-14A, 3B-14B, 3C-14C, and 3D-14D.

In the depicted embodiment of FIG. 2 , device 200 includes substrate202. In the depicted embodiment, substrate 202 is a bulk substrate thatincludes silicon. Alternatively or additionally, the bulk substrateincludes another elementary semiconductor, such as germanium; a compoundsemiconductor, such as silicon carbide, silicon phosphide, galliumarsenide, gallium phosphide, indium phosphide, indium arsenide, indiumantimonide, zinc oxide, zinc selenide, zinc sulfide, zinc telluride,cadmium selenide, cadnium sulfide, and/or cadmium telluride; an alloysemiconductor, such as SiGe, SiPC, GaAsP, AlInAs, AlGaAs, GaInAs, GaInP,and/or GaInAsP; other group III-V materials; other group II-IVmaterials; or combinations thereof. Alternatively, substrate 202 is asemiconductor-on-insulator substrate, such as a silicon-on-insulator(SOI) substrate, a silicon germanium-on-insulator (SGOI) substrate, or agermanium-on-insulator (GOI) substrate. Semiconductor-on-insulatorsubstrates can be fabricated using separation by implantation of oxygen(SIMOX), wafer bonding, and/or other suitable methods. Substrate 202 mayinclude various doped regions. In some examples, substrate 202 includesn-type doped regions (for example, n-type wells) doped with n-typedopants, such as phosphorus (for example, ³¹P), arsenic, other n-typedopant, or combinations thereof. In the depicted implementation,substrate 202 includes p-type doped region (for example, p-type wells)doped with p-type dopants, such as boron (for example, ¹¹B, BF₂),indium, other p-type dopant, or combinations thereof. In someembodiments, substrate 202 includes doped regions formed with acombination of p-type dopants and n-type dopants. The various dopedregions can be formed directly on and/or in substrate 202, for example,providing a p-well structure, an n-well structure, a dual-wellstructure, a raised structure, or combinations thereof. An ionimplantation process, a diffusion process, and/or other suitable dopingprocess can be performed to form the various doped regions.

Device 200 also includes an isolation structure 204 disposed oversubstrate 202. Isolation structure 204 electrically isolates activedevice regions and/or passive device regions of device 200. Isolationstructure 204 can be configured as different structures, such as ashallow trench isolation (STI) structure, a deep trench isolation (DTI)structure, a local oxidation of silicon (LOCOS) structure, orcombinations thereof. Isolation structure 204 includes an isolationmaterial, such as silicon oxide, silicon nitride, silicon oxynitride,other suitable isolation material (for example, including silicon,oxygen, nitrogen, carbon, and/or other suitable isolation constituent),or combinations thereof.

Device 200 further includes semiconductor fins 206 protruding fromsubstrate 202 and the lower portions of semiconductor fins 206 areseparated by isolation structure 204. Each semiconductor fin 206 may besuitable for providing an n-type FET or a p-type FET. In someembodiments, fins 206 as illustrated herein may be suitable forproviding FETs of the same type, i.e., n-type or p-type. Alternatively,they may be suitable for providing FETs of opposite types, i.e., n-typeand p-type. Fins 206 are oriented substantially parallel to one another.Each of fins 206 has at least one channel region and at least one sourceregion and at least one drain region defined along their length in thex-direction, where the at least one channel region is covered by gatestructures 210 and is disposed between the source region and the drainregion. In some embodiments, fins 206 are a portion of substrate 202(such as a portion of a material layer of substrate 202). For example,in the depicted embodiment, where substrate 202 includes silicon, fins206 include silicon. Alternatively, in some embodiments, fins 206 aredefined in a material layer, such as one or more semiconductor materiallayers, overlying substrate 202. For example, fins 206 can include asemiconductor layer stack having various semiconductor layers (such as aheterostructure) disposed over substrate 202. The semiconductor layerscan include any suitable semiconductor materials, such as silicon,germanium, silicon germanium, other suitable semiconductor materials, orcombinations thereof. The semiconductor layers can include same ordifferent materials, etching rates, constituent atomic percentages,constituent weight percentages, thicknesses, and/or configurationsdepending on design requirements of device 200.

Fins 206 are formed by any suitable process including variousdeposition, photolithography, and/or etching processes. An exemplaryphotolithography process includes forming a photoresist layer (resist)overlying substrate 202 (e.g., on a silicon layer), exposing the resistto a pattern, performing a post-exposure bake process, and developingthe resist to form a masking element including the resist. The maskingelement is then used to etch the fin structure into substrate 202. Areasnot protected by the masking element are etched using reactive ionetching (RIE) processes and/or other suitable processes. In someembodiments, fins 206 are formed by patterning and etching a portion ofsilicon substrate 202. In some other embodiments, fins 206 are formed bypatterning and etching a silicon layer deposited overlying an insulatorlayer (for example, an upper silicon layer of asilicon-insulator-silicon stack of an SOI substrate). As an alternativeto traditional photolithography, fins 206 can be formed by adouble-patterning lithography (DPL) process. DPL is a method ofconstructing a pattern on a substrate by dividing the pattern into twointerleaved patterns. DPL allows enhanced feature (e.g., fin) density.Various DPL methodologies include double exposure (e.g., using two masksets), forming spacers adjacent features and removing the features toprovide a pattern of spacers, resist freezing, and/or other suitableprocesses. It is understood that multiple parallel fins 206 may beformed in a similar manner.

In the depicted embodiment of FIG. 2 , various gate structures 210 areformed over fins 206. Gate structures 210 extend along y-direction andtraverse fins 206. Gate structures 210 engage the respective channelregions of fins 206, such that current can flow between the respectiveS/D regions of fins 206 during operation. Each gate structure 210 mayinclude a gate dielectric layer 216 and a gate electrode 212. Gatedielectric layer 216 may include a high-k dielectric material, which isa material having a dielectric constant that is greater than adielectric constant of SiO₂, which is approximately 3.9. In someembodiments, the high-k gate dielectric includes hafnium oxide (HfO₂),which has a dielectric constant that is in a range from approximately 18to approximately 40. In alternative embodiments, the high-k gatedielectric may include ZrO2, Y2O3, La2O5, Gd2O5, TiO2, Ta2O5, HfErO,HfLaO, HfYO, HfGdO, HfAlO, HfZrO, HfTiO, HfTaO, or SrTiO. Gate electrode212 may include a metal-containing material. In some embodiments, themetal gate electrode may include a work function metal component and afill metal component. The work functional metal component is configuredto tune a work function of its corresponding FinFET to achieve a desiredthreshold voltage Vt. In various embodiments, the work function metalcomponent may contain: TiAl, TiAlN, TaCN, TiN, WN, or W, or combinationsthereof. The fill metal component is configured to serve as the mainconductive portion of the functional gate structure. In variousembodiments, the fill metal component may contain Aluminum (Al),Tungsten (W), Copper (Cu), or combinations thereof.

A gate hard mask layer 220 is formed over gate electrode layer 212 andis considered a part of gate structure 210. Gate hard mask layer 220includes any suitable material, for example, SiN, SiC, LaO, AlO, AlON,ZrO, HfO, Si, ZnO, ZrN, ZrAlO, TiO, TaO, YO, TaCN, ZrSi, SiOCN, SiOC,SiCN, HfSi, LaO, SiO, spin-on glass (SOG), a low-k film,tetraethylorthosilicate (TEOS), plasma enhanced CVD oxide (PE-oxide),high-aspect-ratio-process (HARP) formed oxide, other suitable material,or combinations thereof. Gate hard mask layer 220 is formed over gateelectrode layer 212 by any suitable process. For example, a depositionprocess may be performed to form gate hard mask layer 220 over substrate202, fins 206, and isolation structure 204. The deposition processincludes CVD, PVD, ALD, HDPCVD, MOCVD, RPCVD, PECVD, LPCVD, ALCVD,APCVD, plating, other suitable methods, or combinations thereof.

Spacers 214 are located along the sidewalls of gate structures 210.Spacers 214 may include various layers, for example, one or moredielectric layers and pattern layers. In some embodiments, a dielectriclayer is formed conformally over substrate 202, including fins 206 anddummy gate structures. A pattern layer is formed conformally over thedielectric layer. Dielectric layer may include any suitable dielectricmaterial, such as silicon, oxygen, carbon, nitrogen, other suitablematerial, or combinations thereof (for example, silicon oxide, siliconnitride, silicon oxynitride, or silicon carbide, and may be formed byany suitable method, such as ALD, CVD, PVD, other suitable methods, orcombinations thereof. The pattern layer may include any suitablematerial that has a different etch rate than the dielectric layer 220,such as silicon nitride, silicon carboxynitride, other suitabledielectric materials, or combinations thereof. The pattern layer isdeposited by any suitable method, such as ALD, to any suitablethickness. Subsequently, top portions of the dielectric layer and thepattern layers, as well as top portions of dummy gate structures areremoved by a suitable etching process or any other suitable process. Thesuitable etching process, such as a dry etching process, a wet etchingprocess, a reactive ion etching (RIE) process, or combinations thereof.The remaining portions of dielectric layer and pattern layer along dummygate structures form gate spacers 214.

In some embodiments, gate structures 210 are formed by a gatereplacement process after other components (for example, epitaxial S/Dfeatures 250 and first ILD layer 270) of device 200 are fabricated. In agate replacement process, dummy gate structures are formed to wrap thechannel regions of respective fins 206. Each dummy gate structure mayinclude a dummy gate electrode comprising polysilicon (or poly) andvarious other layers, for example, a hard mask layer disposed over dummygate electrode, and an interfacial layer disposed over fins 206 andsubstrate 202, and below dummy gate electrode. After the formation ofepitaxial S/D features 250 as well as first ILD layer 270, dummy gatestructures are removed using one or more etching processes (such as wetetching, dry etching, RIE, or other etching techniques), thereforeleaving openings over the channel regions of fins 206 in place of theremoved dummy gate structures. The opening is then filled with a high-Kdielectric material to form dielectric layer 216 by various processes,such as ALD, CVD, PVD, and/or other suitable process. A metal gatematerial is then deposited over the dielectric material to form themetal gate electrodes 212 of gate structures 210. Gate electrodes 212are formed by various deposition processes, such as ALD, CVD, PVD,and/or other suitable process. Gate hard mask layer 220 is then formedover gate electrode 212 by any suitable deposition process as thoseaforementioned. A CMP process can be performed to remove any excessmaterial of gate dielectric layer 216, gate electrodes 212, and/or gatehard mask layer 220 to planarize gate structures 210.

Device 200 also includes epitaxial S/D features 250 formed in thesource/drain regions of fins 206. For example, semiconductor material isepitaxially grown on fins 206, forming epitaxial S/D features 250 onfins 206. In some embodiments, a fin recess process (for example, anetch back process) is performed on source/drain regions of fins 206,such that epitaxial source/drain features 250 are grown from lower finactive regions. In some other embodiments, source/drain regions of fins206 are not subjected to a fin recess process, such that epitaxialsource/drain features 250 are grown from and wrap at least a portion ofupper fin active regions. In furtherance of some embodiments, epitaxialsource/drain features 250 extend (grow) laterally along the y-direction,such that epitaxial source/drain features 250 are merged epitaxialsource/drain features that span more than one fin. In some embodiments,epitaxial source/drain features 250 include partially merged portionsand/or fully merged portions.

An epitaxy process can implement CVD deposition techniques (for example,vapor-phase epitaxy (VPE), ultra-high vacuum CVD (UHV-CVD), LPCVD,and/or PECVD), molecular beam epitaxy, other suitable SEG processes, orcombinations thereof. The epitaxy process can use gaseous and/or liquidprecursors, which interact with the composition of fins 206. In someembodiments, epitaxial source/drain features 250 are doped with n-typedopants and/or p-type dopants depending on a type of FinFET fabricatedin their respective FinFET device region. For example, in p-type FinFETregion, epitaxial source/drain features 250 can include epitaxial layersincluding silicon and/or germanium, where the silicon germaniumcontaining epitaxial layers are doped with boron, carbon, other p-typedopant, or combinations thereof (for example, forming an Si:Ge:Bepitaxial layer or an Si:Ge:C epitaxial layer). In furtherance of theexample, in n-type FinFET region, epitaxial source/drain features 250can include epitaxial layers including silicon and/or carbon, wheresilicon-containing epitaxial layers or silicon-carbon-containingepitaxial layers are doped with phosphorous, arsenic, other n-typedopant, or combinations thereof (for example, forming an Si:P epitaxiallayer, an Si:C epitaxial layer, or an Si:C:P epitaxial layer). In someembodiments, epitaxial source/drain features 250 include materialsand/or dopants that achieve desired tensile stress and/or compressivestress in the channel regions. In some embodiments, epitaxialsource/drain features 250 are doped during deposition by addingimpurities to a source material of the epitaxy process. In someembodiments, epitaxial source/drain features 250 are doped by an ionimplantation process subsequent to a deposition process. In someembodiments, annealing processes are performed to diffuse dopants inepitaxial source/drain features 250 of device 200.

Still referring to FIGS. 1, 2, and 3A-3D, at operation 104, a firstinterlayer dielectric (ILD) layer 270 is formed over substrate 202.First ILD layer 270 include a material that is different than a materialof gate hard mask layers 220 and spacers 214 to achieve etchingselectivity during subsequent etching processes. First ILD layer 270includes a dielectric material that includes oxygen. For example, firstILD layer 270 includes an oxide layer. In some embodiments, first ILDlayer 270 includes SiO, SiON, TEOS formed oxide, PSG, BPSG, low-kdielectric material (K<3.9), other suitable dielectric material, orcombinations thereof. Exemplary low-k dielectric materials include FSG,carbon doped silicon oxide, Black Diamond® (Applied Materials of SantaClara, Calif.), Xerogel, Aerogel, Parylene, BCB, SiLK (Dow Chemical,Midland, Mich.), polyimide, other low-k dielectric material, orcombinations thereof. First ILD layer 270 may include a multi-layerstructure having multiple dielectric materials and may be formed by adeposition process such as CVD, flowable CVD (FCVD), spin-on-glass(SOG), other suitable methods, or combinations thereof. In someembodiments, an etch stop layer (ESL) may be formed between substrate202 and First ILD layer 270. In some embodiments, ESL 280 includes adielectric material, such as a material that includes silicon andnitrogen (for example, SiN or SiON). The ESL may be formed by adeposition process (such as CVD, FCVD, PVD, ALD, HDPCVD, MOCVD, RPCVD,PECVD, LPCVD, ALCVD, APCVD, plating, other suitable methods, orcombinations thereof). Subsequent to the deposition of the ESL and/orfirst ILD layer 270, a CMP process and/or other planarization process isperformed to planarize the top surface of device 200.

Still referring to FIGS. 1, 2, and 3A-3D, at operation 104, S/D contacts260 are disposed over the S/D regions of fins 206. S/D contacts 260 areportions of a multilayer interconnect (MLI) feature that electricallycouples various devices (for example, transistors, resistors,capacitors, and/or inductors) and/or components (for example, gatestructures and/or source/drain features) of device 200, such that thevarious devices and/or components can operate as specified by designrequirements of device 200. S/D contacts 260 may include any suitableelectrically conductive material, such as Ta, Ti, Al, Cu, Co, W, TiN,TaN, other suitable conductive materials, or combinations thereof.Various conductive materials can be combined to provide S/D contacts 260with various layers, such as one or more barrier layers, adhesionlayers, liner layers, bulk layers, other suitable layers, orcombinations thereof. S/D contacts 260 are formed by patterning firstILD layer 270. Patterning first ILD layer 270 can include lithographyprocesses and/or etching processes to form openings (trenches) in firstILD layer 270. In some embodiments, the lithography processes includeforming a resist layer over first ILD layer 270, exposing the resistlayer to patterned radiation, and developing the exposed resist layer,thereby forming a patterned resist layer that can be used as a maskingelement for etching opening(s) in first ILD layer 270. The etchingprocesses include dry etching processes, wet etching processes, otheretching processes, or combinations thereof. Thereafter, the contactopening(s) are filled with one or more conductive materials. Theconductive material(s) can be deposited by PVD, CVD, ALD,electroplating, electroless plating, other suitable deposition process,or combinations thereof. Thereafter, any excess conductive material(s)can be removed by a planarization process, such as a CMP process,thereby planarizing a top surface of first ILD layer 270 and S/Dcontacts 260.

In the depicted embodiment, referring to FIG. 3D, S/D contacts 260 havea shape of reverse trapezoid in the y-z plane, that is a length alongthe y-direction of the top surface of S/D contacts 260 is greater than alength along the y-direction of the bottom surface of S/D contacts 260.Accordingly, patterned first ILD layer 270 has a shape of trapezoid inthe y-z plane, that is a length along the y-direction of the top surfaceof first ILD layer 270 is less than a length along the y-direction ofthe bottom surface of first ILD layer 270. In some other embodiments,S/D contacts 260 and first ILD layer 270 have other shape(s) in the y-zplane. Shown in FIG. 3D, adjacent fins 206, along with respective S/Dcontacts 260 and epitaxial S/D features 250, are isolated from eachother by first ILD layer 270.

FIGS. 3B-3D show bottom layers 230A, 230B, and 230C of device 200 forillustration purposes only. Bottom layers 230A, 230B, and 230C may becropped from, not shown, or otherwise removed from FIGS. 4A-16 forsimplicity. Bottom layers 230 show different layers in different views.For example, in FIG. 3B, bottom layer 230A includes isolation structure204 and substrate 202; in FIG. 3C, bottom layer 230B includes epitaxialS/D features 250, fins 206 and substrate 202; and in FIG. 3D, bottomlayer 230C includes portions of first ILD layer 270, epitaxial S/Dfeatures 250, fins 206, isolation structure 204, and substrate 202.Bottom layers 230A, 230B, and 230C may include other possible layers, orcombinations thereof.

Now referring to FIGS. 1 and 4A-4D, at operation 106, source/drain (S/D)hard mask layers 265 are formed over S/D contacts 260. Source/drain hardmask layers 265 include a material that is different than a material offirst ILD layer 270 and gate hard mask layers 220 to achieve etchingselectivity during subsequent etching processes. S/D hard mask layers265 include any suitable material, for example, SiC, LaO, AlO, AlON,ZrO, HfO, SiN, Si, ZnO, ZrN, ZrAlO, TiO, TaO, YO, TaCN, ZrSi, SiOCN,SiOC, SiCN, HfSi, LaO, SiO, other suitable material, or combinationsthereof. S/D hard mask layers 265 are formed over S/D contacts 260 byany suitable process. In an exemplary process, S/D contacts 260 arerecessed by a selective etching process that etches S/D contacts 260without (or minimally) etching first ILD layer 270 and gate hard masklayers 220, thereby forming recesses having sidewalls defined by firstILD layer 270 and gate hard mask layers 220 and bottoms defined by topsurfaces of etched back S/D contacts 260. After the selective etching,top surfaces of S/D contacts 260 are lower than a top surface of firstILD layer 270 and top surfaces of gate hard mask layers 220. Adeposition process may then form a S/D hard mask layer over first ILDlayer 270, gate hard mask layers 220, and S/D contacts 260, where theS/D hard mask layer fills recesses formed by the selective etchingprocess. A CMP process may then remove excess S/D hard mask layer, suchas the S/D hard mask layer disposed over first ILD layer 270 and gatehard mask layers 220, thereby forming S/D hard mask layers 265 andexposing the top surface of first ILD layer 270 and the top surfaces ofgate hard mask layers 220. The deposition process for the S/D hard masklayer may include CVD, PVD, ALD, HDPCVD, MOCVD, RPCVD, PECVD, LPCVD,ALCVD, APCVD, plating, other suitable methods, or combinations thereof.

Now referring to FIGS. 1 and 5A-5D, at operation 108, first ILD layer270 is recessed to form openings (trenches) 218. Openings 218 havesidewalls defined by gate spacers 214 of adjacent gate structures 210,gate hard mask layers 220, and adjacent S/D contact structures (here,S/D contacts 260 having S/D hard mask layers 265 disposed thereover).Openings 218 have bottoms defined by the remaining first ILD layer 270.In FIG. 5D, openings 218 have a shape of a trapezoid in the y-z plane,i.e. lengths of tops of openings 218 along the y-direction are shorterthan lengths of bottoms of openings 218 along the y-direction. Recessingfirst ILD layer 270 can include lithography processes and/or etchingprocesses. In some embodiments, the lithography processes includeforming a resist layer over first ILD layer 270, exposing the resistlayer to patterned radiation, and developing the exposed resist layer,thereby forming a patterned resist layer that can be used as a maskingelement for etching first ILD layer 270 to form openings 218. Theetching processes include dry etching processes, wet etching processes,other etching processes, or combinations thereof. In the presentexample, a selective etching process etches a top portion of first ILDlayer 270 without (or minimally) etching spacers 214 and gate hard masklayers 220. In some implementations, an anisotropic etching process isperformed to remove the top portion of first ILD layer 270. A remaining(bottom) portion of first ILD layer 270 is referred to as ILD Lower(ILD_L) layer 270′. ILD_L layer 270′ forms the lower layer of atri-layer ILD layer 278 as shown in FIG. 12B. A top surface of ILD_Llayer 270′ is below top surfaces of spacers 214, top surfaces of gatehard mask layers 220, and top surfaces of S/D contacts 260. For example,a thickness along the z-direction of ILD_L layer 270′, i.e. TL, is about0.5 nm to about 50 nm.

Now referring to FIGS. 1 , FIGS. 6A-6D, FIGS. 7A-7D, and FIGS. 8A-8D, atoperation 110, a second ILD layer 272 is processed to form an ILD Middle(ILD_M) layer 272′ over ILD_L layer 270′. ILD_M layer 272′ forms themiddle layer of tri-layer ILD layer 278 as shown in FIG. 12B. Turning toFIGS. 6A-6D, second ILD layer 272 is deposited over substrate 202.Second ILD layer 272 fills openings 218 and is disposed on ILD_L layer270′. Second ILD layer 272 may include a material different from gatespacers 214, gate hard mask layer 220, S/D contact 260, and S/D hardmask layer 265 to achieve etching selectivity during subsequent etchingprocesses. In some embodiments, the material of second ILD layer 272 isdifferent from the material of first ILD layer 270, such that thematerial of second ILD layer 272 may impart ILD_M layer 272′ with animproved contact to contact TDDB window between adjacent S/D contacts260. Second ILD layer 272 includes any suitable material, for example,SiC, LaO, AlO, AlON, ZrO, HfO, SiN, Si, ZnO, ZrN, ZrAlO, TiO, TaO, YO,TaCN, ZrSi, SiOCN, SiOC, SiCN, HfSi, LaO, SiO, other suitable material,or combinations thereof. Second ILD layer 272 is formed over substrate202 by a deposition process, such as CVD, PVD, ALD, HDPCVD, MOCVD,RPCVD, PECVD, LPCVD, ALCVD, APCVD, plating, other suitable methods, orcombinations thereof.

In some embodiments, referring to FIGS. 6D and 16 , one or more centralvoids 273M and boundary voids 273S may occur during the deposition ofsecond ILD layer 272, particularly when openings 218 have trapezoidalshapes in the y-z plane. In some embodiments, central voids 273M mayoccur in the middle of opening 218 when filling in the material ofsecond ILD layer 272. Central voids 273M are formed when the middle ofopenings 218 are not completely filled by second ILD layer 272. In someother embodiments, boundary voids 273S may occur at the bottom sidecorners of opening 218 when filling in the material of second ILD layer272. Boundary voids 273S are formed when corners of openings 218 are notcompletely filled by second ILD layer 272. Boundary voids 273S aredefined between S/D contacts 260, ILD_L layers 270′, and second ILDlayer 272. In yet some other embodiments, central voids 273M andboundary voids 273S may occur in the middle of opening 218 and at thebottom side corners of opening 218, respectively, when filling in thematerial of second ILD layer 272. Central voids 273M and boundary voids273S may have a width in the y-direction and a height in thez-direction. The width of central voids 273M and boundary voids 273S is0 nm to about 30 nm, and the height of central voids 273M and boundaryvoids 273S is 0 nm to about 30 nm. A distance of a bottom surface ofcentral void 273M to the top surface of ILD_L layer 270′ in thez-direction is 0 nm to about 60 nm. A relatively slow deposition processor a high temperature deposition process (for example, a deposition at atemperature of about 150° C. to about 550° C.) may reduce the occurrenceof central voids 273M and boundary voids 273S.

Referring to FIGS. 1 and 7A-7D, still at operation 110, any excessmaterial(s) of second ILD layer 272 may be removed by a planarizationprocess, such as a CMP process or an etching process, therebyplanarizing a top surface of device 200. In some embodiment, aplanarization process is performed to remove excess second ILD layer272, such as second ILD layer 272 disposed over gate hard mask layers220 and S/D hard mask layer 265, thereby exposing top surfaces of gatehard mask layers 220 and top surfaces of S/D hard mask layer 265.

Referring to FIGS. 1 and 8A-8D, still at operation 110, second ILD layer272 is recessed to form openings (trenches) 228. Openings 228 havesidewalls defined by spacers 214, gate hard mask layers 220 of adjacentgate structures 210, and adjacent S/D contact structures (here, S/Dcontacts 260 and S/D hard mask features 265 disposed thereover). Bottomsof openings 228 are defined by the recessed second ILD layer 272. InFIG. 8D, openings 228 have a shape of a trapezoid in the y-z plane, i.e.lengths of tops of openings 228 along the y-direction are shorter thanlengths of bottoms of openings 228 along the y-direction Recessingsecond ILD layer 272 can include lithography processes and/or etchingprocesses. In some embodiments, the lithography processes includeforming a resist layer over second ILD layer 272, exposing the resistlayer to patterned radiation, and developing the exposed resist layer,thereby forming a patterned resist layer that can be used as a maskingelement for etching second ILD layer 272 to form openings 228. Theetching processes include dry etching processes, wet etching processes,other etching processes, or combinations thereof. In the presentexample, a selective etching process etches a top portion of second ILDlayer 272 without (or minimally) etching spacers 214, gate hard masklayers 220, S/D hard mask layers 265, and/or S/D contacts 260. In someimplementations, an anisotropic etching process is performed to removethe top portion of second ILD layer 272. A remaining (bottom) portion ofsecond ILD layer 272 is referred to as ILD Middle (ILD_M) layer 272′. Atop surface of ILD_M layer 272′ is below top surfaces of spacers 214 andtop surfaces of gate hard mask layers 220. In the depicted embodiment,the top surface of ILD_M layer 272′ is below top surfaces of S/Dcontacts 260, though the present disclosure contemplates embodiments,where the top surface of ILD_M layer 272′ is above top surfaces of S/Dcontacts 260. A thickness of ILD_M layer 272′ along the z-direction,i.e. TM, is about 0.5 nm to about 50 nm. As depicted in FIG. 8D,recessing second ILD layer 272 modifies central void 273M into a centralvoid 273C defined by a recessed portion of a top surface of ILD_M layer272′. Central void 273C is disposed in a top middle portion of ILD_Mlayer 272′. Referencing FIG. 8D, central voids 273C are defined betweenthe top surface of ILD_M layer 272′ and the surrounding ILD_M layer 272′bulk volume.

Now referring to FIGS. 1 , FIGS. 9A-9D, and FIGS. 10A-10D, at operation112, a third ILD layer 274 is processed to form an ILD Upper (ILD_U)layer 274′ over ILD_M layer 272′. ILD_U layer 274′ forms the upper layerof tri-layer ILD layer 278 as shown in FIG. 12B. Turning to FIGS. 9A-9D,third ILD layer 274 fills openings 228, and is disposed on ILD_M layer272′. Third ILD layer 274 includes a material different from ILD_M layer272′, gate hard mask layer 220, and S/D hard mask layer 265. Using adifferent material for ILD layer 274 imparts ILD_U layer 274′ withdifferent etching selectivity compared to ILD_M layer 272′, gate hardmask layer 220, and S/D hard mask layer 265. In other embodiments,material of ILD_M layer 272′, material of gate hard mask layer 220, andmaterial of source/drain hard mask layer 265 may match each other(having matching etching selectivity). In that case, material of thirdILD layer 274 would still include a material different from ILD_M layer272′, gate hard mask layer 220, and S/D hard mask layer 265 in order tomaintain etching selectivity. Third ILD layer 274 includes any suitablematerial, for example, SiC, LaO, AlO, AlON, ZrO, HfO, SiN, Si, ZnO, ZrN,ZrAlO, TiO, TaO, YO, TaCN, ZrSi, SiOCN, SiOC, SiCN, HfSi, LaO, SiO,other suitable material, or combinations thereof. Third ILD layer 274 isformed over substrate 202 by any suitable process. For example, adeposition process may be performed to form second ILD layer 272. Thedeposition process may include CVD, PVD, ALD, HDPCVD, MOCVD, RPCVD,PECVD, LPCVD, ALCVD, APCVD, plating, other suitable methods, orcombinations thereof.

Now referring to FIGS. 10D and 16 , in some embodiments, one or morecentral voids 275M and boundary voids 275S may occur during depositionof third ILD layer 274, specifically when opening 228 has a shape oftrapezoid in the y-z plane. In some embodiments, central voids 275M mayoccur in the middle, or center, of opening 228 when filling in thematerial of third ILD layer 274. Central voids 275M are formed when themiddle of openings 228 are not completely filled by third ILD layer 274.In some other embodiments, boundary voids 275S may occur at the bottomside corners of opening 228 when filling in the material of third ILDlayer 274. Boundary voids 275S are formed when corners of openings 228are not completely filled by third ILD layer 274. Boundary voids 275Sare defined between S/D contacts 260 and/or S/D hard mask layers 265,ILD_M layers 272′, and third ILD layer 274. In yet some otherembodiments, central voids 275M and boundary voids 275S may occur in themiddle of opening 228 and at the bottom side corners of opening 228,respectively, when filling in the material of third ILD layer 274.Central voids 275M and boundary voids 275S may have a width in they-direction and a height in the z-direction. The width of central voids275M and boundary voids 275S is 0 nm to about 30 nm; and, the height ofcentral voids 275M and boundary voids 275S is 0 nm to about 30 nm. Adistance of a bottom surface of central void 275M to the top surface ofILD_L layer 270′ in the z-direction is 0 nm to about 70 nm. A relativelyslow deposition process or a high temperature deposition process (forexample, a deposition at temperature of about 150° C. to about 550° C.)may reduce the occurrence of central voids 275M and boundary voids 275S.

Referring to FIGS. 1 and 10A-10D, still at operation 112, any excessmaterial(s) of third ILD layer 274 may be removed by a planarizationprocess, such as a CMP process or an etching process, therebyplanarizing a top surface of device 200. In some embodiments, theplanarization process is performed to remove excess third ILD layer 274,such as third ILD layer 274 disposed over gate hard mask layers 220 andS/D hard mask layers 265, thereby exposing top surfaces of gate hardmask layers 220 and top surfaces of source/drain hard mask layers 265. Aremaining portion of third ILD layer 274 is referred to as ILD Upper(ILD_U) layer 274′. A top surface of ILD_U layer 274′ is substantiallyplanar with top surfaces of gate hard mask layers 220 and top surfacesof S/D hard mask layers 265. In some embodiments, along the z-direction,the top surface of ILD_U layer 274′ is higher than top surface ofspacers 214. In some embodiments, a thickness of ILD_U layer 274′ alongthe z-direction, i.e. TU, is about 0.5 nm to about 50 nm.

Accordingly, ILD_L layer 270′, ILD_M layer 272′, and ILD_U layer 274′together form a tri-layer ILD layer 278 in device 200. In the depictedembodiment, the tri-layer ILD layer 278 is a bottommost ILD layer (ILD0)of the MLI structure. As described below, configuring a device-level ILDlayer of the MLI structure as tri-layer ILD layer increases processingflexibility when forming vias to S/D contacts 260 and/or metal gates212. A top surface of the tri-layer ILD feature (top surface of ILD_Ulayer 274′) is higher than a top surface of spacers 214 in thez-direction and is substantially the same height as gate hard mask layer220 and S/D hard mask layer 265. In some embodiments, a proper thicknessration between each two layers of the tri-layer ILD layer should beconsidered according to the design requirements of device 200. Forexample, a thickness ratio of ILD_L layer 270′ to ILD_M layer 272′ isabout 10% to 250%; a thickness ratio of ILD_L layer 270′ to ILD_U layer274′ is about 10% to 250%; and a thickness ratio of ILD_M layer 272′ toILD_U layer 274′ is about 30% to 300%. If the thickness of the bottomlayer is too large, it may not provide enough space for the middle layer(which should be below the top surface of the spacers) and the upperlayer (which should has a portion below the spacers); if the thicknessof the middle layer (ILD_M layer 272′) is too large, it may not be belowthe top surface of the spacer; and if the thickness of the upper layer(ILD_U layer 274′) is too large, it may limit the thickness of themiddle layer to provide enough contact to contact TDDB window. And, thethickness of each layer cannot be too small to make the thicknesscontrol too difficult. Also, the thickness of the bottom layer should belarge enough to provide isolation between gates; the thickness of themiddle layer should be large enough to provide enough contact to contactTDDB window; and the thickness of the upper layer should be large enoughsuch that the upper layer can extend from below the top surface of thespacers to above the top surface of the spacers to provide differentetching selectivity than the hard mask layer.

Now referring to FIGS. 1 and 11A-11D, at operation 114, an etch stoplayer (ESL) 280 is formed over tri-layer ILD layer 278. In someembodiments, ESL 280 includes a dielectric material, such as a materialthat includes silicon and nitrogen (for example, SiN or SiON). Also atoperation 114, a fourth ILD layer 285 is formed over ESL 280. In someembodiments, fourth ILD layer 285 includes a dielectric materialincluding, for example, SiO, SiN, SiON, TEOS formed oxide, PSG, BPSG,low-k dielectric material (K<3.9), other suitable dielectric material,or combinations thereof. Exemplary low-k dielectric materials includeFSG, carbon doped silicon oxide, Black Diamond® (Applied Materials ofSanta Clara, Calif.), Xerogel, Aerogel, amorphous fluorinated carbon,Parylene, BCB, SILK (Dow Chemical, Midland, Mich.), polyimide, otherlow-k dielectric material, or combinations thereof. Fourth ILD layer 285includes a dielectric material different than ESL 280. In someembodiments, where ESL 280 includes silicon and nitride, fourth ILDlayer 285 includes a low-k dielectric material different than thedielectric material of ESL 280. In some embodiments, fourth ILD layer285 may have a multilayer structure having multiple dielectricmaterials. Fourth ILD layer 285 and/or ESL 280 are formed over substrate202, for example, by a deposition process (such as CVD, FCVD, PVD, ALD,HDPCVD, MOCVD, RPCVD, PECVD, LPCVD, ALCVD, APCVD, plating, othersuitable methods, or combinations thereof). Subsequent to the depositionof ESL 280 and/or fourth ILD layer 285, a CMP process and/or otherplanarization process is performed to planarize the top surface ofdevice 200.

Now referring to FIGS. 1 and 12A-12D, at operation 116, gate contactopenings 290 and/or S/D contact openings 292 are formed through fourthILD layer 285 and ESL 280. Contact openings 290 and 292 are formed byany suitable process including various photolithography, and/or etchingprocesses. An exemplary photolithography process includes forming aphotoresist layer (resist) overlying fourth ILD layer 285, exposing theresist to a pattern, performing a post-exposure bake process, anddeveloping the resist to form a masking element including the resist.The masking element is then used to etch the contact openings 290 and292 into fourth ILD layer 285 and ESL 280. Thereafter, the maskingelement is removed to expose fourth ILD layer 285. Alternatively, doublepatterning and/or multiple patterning processes can be implemented toform gate contact openings 290 and/or S/D contact openings 292. Aselective etching process is then performed to remove gate hard masklayer 220 exposed in gate contact opening 290. The etching process toselectively etch gate hard mask layer 220 relative to ILD_U layer 274′can be referred to as slot Vg etching, shown in FIG. 12B. Selectiveetching is also performed to remove S/D hard mask layer 265 exposed inS/D contact opening 292. The etching process to selectively etch S/Dhard mask layer 265 relative to ILD_U layer 274′ can be referred to asslot Vd etching, shown in FIG. 12D. The slot Vg and/or slot Vd etchingprocess can include a dry etching process (for example, a reactive ionetching (RIE) process), a wet etching process, other suitable etchingprocess, or combinations thereof. Portions of gate hard mask layer 220and/or S/D hard mask layer 265 may or may not remain based on the maskelement used to selectively etch gate hard mask layer 220 and/or S/Dhard mask layer 265. For example, as depicted in FIG. 12B showing slotVg etching, gate hard mask layer 220 exposed in gate contact opening 290is completely removed. However, as depicted in FIG. 12D showing slot Vdetching, side portions of the respective S/D hard mask layer 265 exposedin S/D contact opening 292 remain after the selective etching processsince these side portions are covered by the masking element. Thepatterned resist layer can be removed before or after the etchingprocess. In some embodiments, the exposure process can implementmaskless lithography, electron-beam writing, ion-beam writing and/ornanoprint technology.

Conventional semiconductor devices implement a one-layer ILD layer (forexample, only ILD layer 270) as the device-level (bottommost) dielectriclayer of the MLI structure. It has been observed that metal bridgingissues arise from such configurations due to the resolution limit andthe insufficient etching selectivity between the one-layer ILD layer andgate hard mask layers and/or S/D hard mask layers. For example, in theconventional semiconductor structure, due to the scaling down of ICdimensions, pattern shifting may be happened during fabrication. Sinceno sufficient etching selectivity is provided between the gate hardmasks (e.g. 220) and the ILD layer (e.g. 270), the slot Vg etchingprocess at operation 116 to form the gate opening 290 will not onlyremove gate hard mask layers, but also a top portion of the ILD layer.Similar situation may happen when removing the S/D hard masks (e.g.265), i.e. a top portion of the ILD layer may also be removed.Therefore, the one-layer ILD layer is recessed, unintentionally formingopenings between adjacent spacers 214 (in other words, a height of theone-layer ILD layer in the z-direction is lower than a height of spacers214). This will cause metal bridge issues after depositing the metalmaterial(s) in the contact openings to form vias to the metal gatesand/or S/D contacts, because metal material will fill the openingsbetween adjacent spacers 214 and may interconnect the vias and the metalgates and/or S/D contacts.

However, the tri-layer structure of the device-level ILD layer in thepresent disclosure can provide sufficient etching selectivity betweenthe device-level ILD layer and the gate (or S/D) hard mask to mitigatethe metal bridge issues. In some embodiment, it may also improve thecontact to contact TDDB window. As depicted in FIG. 12B for slot Vgetching and 12D for slot Vd etching, since device 200 includes tri-layerILD layer 278 (including ILD_L layer 270′, ILD_M layer 272′, and ILD_Ulayer 274′) and the material of ILD_U layer 274′includes a materialhaving different etching selectivity than gate hard mask layer 220 andS/D hard mask layer 265, the selective etching process only removes gatehard mask layers 220 exposed in gate contact opening 290 and S/D hardmask layers 265 exposed in S/D contact openings 292, for each of slot Vgetching and slot Vd etching, respectively. The tri-layer ILD layer 278is substantially unaffected either by the slot Vg etching process usedto remove gate hard mask layer 220 exposed in gate contact opening 290,or by the slot Vd etching process used to remove S/D hard mask layer 265exposed in S/D contact opening 292. That is, a height of the tri-layerILD layer 278 in the z-direction is greater than a height of spacers214, such that a top surface of the tri-layer ILD layer 278 is above topsurfaces of spacers 214. Therefore, metal material formed in gateopening 290 and/or S/D contact openings 292 is not formed betweenadjacent spacers 214, preventing the metal bridge issues observed withone-layer ILD layers. In addition, the material of ILD_M layer 272′ inthe tri-layer ILD layer can be used to improve the contact to contactTDDB window, thereby extending the life of device 200. Therefore, thetri-layer structure of the device-level ILD layer provides moremanufacturing flexibility to not only mitigate the metal bridge issue,but also improve the TDDB window of the device.

Now referring to FIGS. 1 and 13A-13D, at operation 118, metal materialsare filled in gate contact openings 290 and/or S/D contact openings 292to form gate vias 294 and/or S/D vias 295. Vias 294 and 295 are portionsof the MLI feature that electrically couples various devices and/orcomponents of device 200. Vias 294 and 295 may include any suitableelectrically conductive material, such as Ta, Ti, Al, Cu, Co, W, TiN,TaN, other suitable conductive materials, or combinations thereof.Various conductive materials can be combined to provide vias 294 and 295with various layers, such as one or more barrier layers, adhesionlayers, liner layers, bulk layers, other suitable layers, orcombinations thereof. Vias 294 and 295 are formed by filling contactopenings 290 and 292 with one or more conductive materials. Theconductive material(s) can be deposited by PVD, CVD, ALD,electroplating, electroless plating, other suitable deposition process,or combinations thereof. Thereafter, one or more polishing processes(for example, CMP) may be performed to remove the top portion of vias294 and 295 and to remove ESL 280 and fourth ILD layer 285. This resultsin the top surface of device 200 being planarized down to a level of thetop surfaces of gate hard mask layers 220, ILD_U layer 274′, S/D contacthard mask layer 265, and vias 294 and 295.As depicted in FIG. 13B, eachof gate vias 294 includes a top portion and a bottom portion. Sidewallsof the top portions of gate vias 294 directly contact the upper layer274′ of tri-layer ILD layer 278; and sidewalls of the bottom portions ofgate vias 294 directly contact the spacers 214. Thereby, gate vias 294are separated by tri-layer ILD layer 278 as well as the gate spacers214. Similarly, as depicted in FIG. 13D, sidewalls of S/D vias 295directly contact the upper layer 274′ of tri-layer ILD layer 278.Thereby, S/D vias 295 are separated by tri-layer ILD layer 278.

Now referring to FIGS. 1 and 14A-14D, other processes may be performedto complete the fabrication of device 200. For example, another etchstop layer (ESL) 296 is formed on the top surface of device 200. And,another ILD layer 297 is formed over the ESL 296. Materials andfabrication process of ESL 296 and ILD layer 297 are similar as thosediscussed above regarding ESL 280 and ILD layer 285 in FIGS. 11A-11D.Conductive lines 298 may then be formed in the ESL 296 and ILD layer 297as depicted in FIGS. 14A-14D. Conductive material of the metal line 298may include Ta, TaN, Ti, TiN, Cu, Co, Ru, Mo, W, other conductivematerial, or combinations thereof. Forming of conductive lines 298 mayinclude several steps, such as photoresist, etching, deposition, etc.Thereafter, a planarization process (e.g. CMP) is performed to planarizethe top surface of device 200. Subsequently, further processes areperformed. For example, other contacts, vias, conductive lines, andinterlayer dielectrics may be formed over the substrate, configured toconnect the various features to form a functional circuit that mayinclude one or more semiconductor structures.

Now referring to FIGS. 15A-15P, different tri-layer ILD layer 278configurations featuring different voids are illustrated. FIG. 15Aincludes voids 273C (central void in ILD_M layer 272′), 273S (boundaryvoids in ILD_M layer 272′), 275M (central void in ILD_U layer 274′), and275S (boundary voids in ILD_U layer 274′). FIG. 15B includes voids 273C,273S, 275M but not 275S. FIG. 15C includes voids 273C, 273S, 275S butnot 275M. FIG. 15D includes voids 273C, 273S but not 275S, 275M. FIG.15E includes voids 273C, 275M, 275S but not 273S. FIG. 15F includesvoids 273C, 275M but not 273S, 275S. FIG. 15G includes voids 273C, 275Sbut not 273S, 275M. FIG. 15H includes voids 273C but not 273S, 275M,275S. FIG. 15I includes voids 273S, 275M, 275S but not 273C. FIG. 15Jincludes voids 273S, 275M but not 273C, 275S. FIG. 15K includes voids273S, 275S but not 273C, 275M. FIG. 15L includes voids 273S but not273C, 275M, 275S. FIG. 15M includes voids 275M, 275S but not 273C, 273S.FIG. 15N includes voids 275M but not 273C, 273S, 275S. FIG. 15O includesvoids 275S but not 273C, 273S, 275M. FIG. 15P does not include voids273C, 273S, 275M, 275S.

Fabrication of device 200 can continue. For example, it may form othercontact openings, contact metal, as well as various contacts, vias,wires, and multilayer interconnect features (e.g., metal layers andinterlayer dielectrics) over device 200, configured to connect thevarious features to form a functional circuit that may include one ormore multi-gate devices.

Although not intended to be limiting, one or more embodiments of thepresent disclosure provide many benefits to a semiconductor device and aformation process thereof. For example, embodiments of the presentdisclosure provide a semiconductor device with a tri-layer ILD feature.Top layer of the tri-layer ILD provides an etching selectivity with thegate hard mask layer and/or S/D hard mask layer. Top layer of thetri-layer ILD also provides an etching selectivity with the middle layerof the three-layer ILD. Compare with one-layer ILD feature, thetri-layer ILD feature is not substantially affected when selectiveremoving the gate hard mask layer and/or S/D hard mask layer exposed inthe contact openings during the fabrication. Thus, metal bridge issuescaused by the partially removed on-layer ILD feature during thefabrication can be avoided. In addition, the middle layer of thetri-layer ILD feature can improve the contact to contact TDDB windowsuch that to extend the device life.

The present disclosure provides for many different embodiments.Semiconductor device having multi-layer dielectric feature and methodsof fabrication thereof are disclosed herein. An exemplary semiconductordevice comprises a fin disposed over a substrate and a gate structuredisposed over a channel region of the fin, such that the gate structuretraverses source/drain regions of the fin. The exemplary semiconductordevice further comprises a device-level interlayer dielectric (ILD)layer of a multi-layer interconnect structure disposed over thesubstrate, wherein the device-level ILD layer includes a firstdielectric layer, a second dielectric layer disposed over the firstdielectric layer, and a third dielectric layer disposed over the seconddielectric layer, and a material of the third dielectric layer isdifferent than a material of the second dielectric layer and a materialof the first dielectric layer. The exemplary semiconductor devicefurther comprises a gate contact to the gate structure disposed in thedevice-level ILD layer and a source/drain contact to the source/drainregions disposed in the device-level ILD layer.

In some embodiments, the exemplary semiconductor device furthercomprises a material of the second dielectric layer is different than amaterial of the first dielectric layer. In some embodiments, the gatestructure includes a gate electrode and spacers disposed along sidewallsof the gate electrode, the material of the third dielectric layer of thedevice-level ILD layer is different than a material of the spacers, andthe material of the third dielectric layer of the device-level ILD layeris different than a material of the source/drain contacts. In somefurther embodiments, a top surface of the second dielectric layer of thedevice-level ILD layer is below a top surface of the spacers of the gatestructure and a top surface of the of the third dielectric layer of thedevice-level ILD layer is above a top surface of the spacers of the gatestructure. In some further embodiments, a thickness ratio of the firstdielectric layer to the second dielectric layer is about 10% to about250%, a thickness ratio of the first dielectric layer to the thirddielectric layer is about 10% to about 250%, and a thickness ratio ofthe second dielectric layer to the third dielectric layer is about 30%to about 300%. In some embodiments, the semiconductor device furthercomprises a S/D hard mask disposed over the S/D contact, wherein thematerial of the third dielectric layer of the device-level ILD layer isdifferent than a material of the S/D hard mask. And in some embodiments,an etch stop layer disposed between the first dielectric layer of thedevice-level ILD layer and the substrate.

Another exemplary semiconductor device comprises a fin disposed over asubstrate, and a first gate structure and a second gate structuredisposed over channel regions of the fin and traversing source/drainregions of the fin, wherein the first gate structure and the second gatestructure each include a gate electrode and spacers disposed alongsidewalls of the gate electrode. The another exemplary semiconductordevice further comprises a S/D contact disposed over at least one of thesource/drain regions of the fin and a tri-layer interlayer dielectric(ILD) layer disposed between the first gate structure and the secondgate structure, wherein the tri-layer ILD layer includes a lower layer,a middle layer disposed over the lower layer, and an upper layerdisposed over the middle layer, wherein the upper layer includes amaterial different than a material of the lower layer and a material ofthe middle layer. The another exemplary semiconductor device furthercomprises gate vias disposed over the gate electrodes of the first gatestructure and the second gate structure, wherein the gate vias directlycontact the upper layer of the tri-layer ILD layer.

In some embodiments, a top surface of the middle layer of the tri-layerILD layer is below a top surface of the spacers and a top surface of theupper layer of the tri-layer ILD layer is above a top surface of thespacers. In some embodiments, a material of the middle layer of thetri-layer ILD layer has a different etching selectivity than a materialof the lower layer of the tri-layer ILD layer. In some embodiments, themiddle layer of the tri-layer ILD layer includes a central void locatedin a top middle portion of the middle layer of the tri-layer ILD layer.In some embodiments, the middle layer of the tri-layer ILD layerincludes a boundary void located in a bottom corner of the middle layerof the tri-layer ILD layer. In some embodiments, the upper layer of thetri-layer ILD layer includes a central void located in a middle portionof the upper layer of the tri-layer ILD layer. In some embodiments, theupper layer of the tri-layer ILD layer includes a boundary void locatedin a bottom corner portion of the upper layer of the tri-layer ILDlayer.

In some embodiments, the another exemplary semiconductor device furthercomprising a S/D via disposed over the S/D contact, wherein the S/D viadirectly contacts the upper layer of the tri-layer ILD layer.

An exemplary method includes forming a first dielectric layer over asubstrate, wherein a top surface of the first dielectric layer issubstantially planar with a top surface of a first gate structuredisposed over the substrate and a top surface of a second gate structuredisposed over the substrate; recessing the first dielectric layer toform an opening between the first gate structure and the second gatestructure, wherein a top surface of the recessed first dielectric layeris lower than the top surface of the first gate structure and the topsurface of the second gate structure; forming a second dielectric layerin the opening over the first dielectric layer, wherein a top surface ofthe second dielectric layer is lower than the top surface of the firstgate structure and the top surface of the second gate structure; forminga third dielectric layer in an opening over the second dielectric layer,wherein a top surface of the third dielectric layer is substantiallyplanar with the top surface of the first gate structure and the topsurface of the second gate structure, a material of the third dielectriclayer is different than a material of the second dielectric layer andthe first dielectric layer, and the first dielectric layer, the seconddielectric layer, and the third dielectric layer combine to form adevice-level interlayer dielectric (ILD) layer.

In some embodiments, each of the first gate structure and the secondgate structure include a gate electrode, spacers disposed alongsidewalls of the gate electrode, and a gate hard mask layer disposedover the gate electrode and the spacers, wherein a material of the gatehard mask layer and a material of the spacers are different than amaterial of the first dielectric layer of the device-level ILD layer,and recessing the first dielectric layer includes selectively etchingthe first dielectric layer to form the opening. In some embodiments, thematerial of the gate hard mask layer is different than a material of thethird dielectric layer of the device-level ILD layer, and the exemplarymethod further comprises selectively removing the gate hard mask layerof the first gate structure and the second gate structure to form a gatecontact opening; depositing a conductive material in the gate contactopening; and planarizing a top surface of the conductive material toexpose the third dielectric layer of the device-level ILD layer.

In some embodiments, the exemplary method further comprises forming asource/drain contact over the substrate; and forming a source/drain hardmask layer over the source/drain contact, wherein the source/drain hardmask layer includes a material different than the material of the thirddielectric layer of the device-level ILD layer, and a top surface of thesource/drain hard mask layer is substantially planar with the topsurface of the first gate structure and the top surface of the secondgate structure.

In some embodiments, the exemplary method further comprises selectivelyremoving the source/drain hard mask layer to form a S/D contact opening;depositing a conductive material in the S/D contact opening; andplanarizing a top surface of the conductive material to expose the thirddielectric layer of the device-level ILD layer.

The foregoing outlines features of several embodiments so that thoseskilled in the art may better understand the aspects of the presentdisclosure. Those skilled in the art should appreciate that they mayreadily use the present disclosure as a basis for designing or modifyingother processes and structures for carrying out the same purposes and/orachieving the same advantages of the embodiments introduced herein.Those skilled in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the presentdisclosure, and that they may make various changes, substitutions, andalterations herein without departing from the spirit and scope of thepresent disclosure.

What is claimed is:
 1. A semiconductor device, comprising: a multilayerdielectric layer having a lower layer, a middle layer, and an upperlayer, wherein a composition of the middle layer is different than acomposition of the upper layer and a composition of the lower layer; agate structure disposed in the multilayer dielectric layer, wherein thegate structure is disposed between a first epitaxial source/drain and asecond epitaxial source/drain along a first direction, the gatestructure extends lengthwise along a second direction, and the seconddirection is different than the first direction; a source/draininterconnect disposed in the multilayer dielectric layer, wherein thesource/drain interconnect includes a source/drain contact and asource/drain via, the source/drain interconnect connects the firstepitaxial source/drain to a conductive line, and the source/drain via isbetween the source/drain contact and the conductive line; and wherein:in a first cross-sectional view along the first direction, thesource/drain interconnect is disposed between a first gate spacer and asecond gate spacer, and in a second cross-sectional view along thesecond direction, the source/drain interconnect is disposed between afirst portion of the multilayer dielectric layer and a second portion ofthe multilayer dielectric layer.
 2. The semiconductor device of claim 1,wherein a thickness of the source/drain via is less than a thickness ofthe upper layer of the multilayer dielectric layer, wherein the upperlayer of the multilayer dielectric layer physically contacts thesource/drain via and the source/drain contact.
 3. The semiconductordevice of claim 1, wherein a source/drain hard mask layer is disposedbetween the source/drain via and the multilayer dielectric layer and acomposition of the source/drain hard mask layer is different than thecomposition of the upper layer of the multilayer dielectric layer. 4.The semiconductor device of claim 1, wherein at least one void isbetween the multilayer dielectric layer and the source/drain contact. 5.The semiconductor device of claim 4, wherein the at least one voidincludes a void between the source/drain contact, the upper layer of themultilayer dielectric layer, and the middle layer of the multilayerdielectric layer.
 6. The semiconductor device of claim 4, wherein the atleast one void includes a void between the source/drain contact, themiddle layer of the multilayer dielectric layer, and the lower layer ofthe multilayer dielectric layer.
 7. The semiconductor device of claim 4,wherein the at least one void has a maximum dimension that is less thanabout 30 nm.
 8. The semiconductor device of claim 1, wherein at leastone void is within the multilayer dielectric layer.
 9. The semiconductordevice of claim 8, wherein the at least one void has a maximum dimensionof about 30 nm.
 10. The semiconductor device of claim 8, wherein the atleast one void includes a void within the upper layer of the multilayerdielectric layer.
 11. The semiconductor device of claim 10, wherein amaximum distance between the void and a top surface of the lower layerof the multilayer dielectric layer is about 70 nm.
 12. The semiconductordevice of claim 8, wherein the at least one void includes a void withinthe middle layer of the multilayer dielectric layer.
 13. Thesemiconductor device of claim 12, wherein a maximum distance between thevoid and a top surface of the lower layer of the multilayer dielectriclayer is about 60 nm.
 14. A semiconductor device, comprising: amultilayer dielectric layer disposed over a fin structure extending froma substrate, wherein the multilayer dielectric layer has a lower layerhaving a first composition, a middle layer having a second composition,and an upper layer having a third composition, wherein the secondcomposition is different than the third composition; and a first gatestructure, a second gate structure, a first source/drain contact, asecond source/drain contact, a gate via disposed over the second gatestructure, a source/drain via disposed over the first source/draincontact, a gate hard mask disposed over the first gate structure, and asource/drain hard mask disposed over the second source/drain contact,wherein: the first gate structure, the second gate structure, the firstsource/drain contact, and the second source/drain contact are disposedin the upper layer, the middle layer, and the lower layer of themultilayer dielectric layer, the gate via, the source/drain via, thegate hard mask, and the source/drain hard mask are disposed in the upperlayer of the multilayer dielectric layer, the gate hard mask has afourth composition, the source/drain hard mask has a fifth composition,the fourth composition is different than the third composition, and thefifth composition is different than the third composition, in a firstcross-sectional view along a lengthwise direction of the fin structure,the first gate structure and the second gate structure are disposed overan isolation structure disposed over the substrate, the multilayerdielectric layer is disposed along sidewalls of the first gatestructure, and the multilayer dielectric layer is disposed alongsidewalls of the second gate structure, and in a second cross-sectionalview along the lengthwise direction of the fin structure, the first gatestructure, the second gate structure, the first source/drain contact,and the second source/drain contact are disposed over the fin structure,the first source/drain contact is adjacent to the first gate structure,and the second source/drain contact is adjacent to the second gatestructure.
 15. The semiconductor device of claim 14, wherein in a thirdcross-sectional view along a widthwise direction of the fin structure,the first source/drain contact is disposed over the fin structure andthe multilayer dielectric layer is disposed along sidewalls of the firstsource/drain contact and the source/drain via.
 16. The semiconductordevice of claim 15, wherein the source/drain via has a first sidewalland a second sidewall, wherein the first sidewall physically contactsthe upper layer of the multilayer dielectric layer and a residualsource/drain hard mask is between the second sidewall and the upperlayer of the multilayer dielectric layer.
 17. The semiconductor deviceof claim 14, wherein the second composition, the fourth composition, andthe fifth composition are the same.
 18. The semiconductor device ofclaim 14, wherein a thickness of the middle layer of the multilayerdielectric layer and a thickness of the upper layer of the multilayerdielectric layer are each about 0.5 nm to about 50 nm.
 19. Asemiconductor device comprising: a first gate structure and a secondgate structure disposed over a substrate, wherein the first gatestructure has a first gate stack and first gate spacers disposed alongsidewalls of the first gate stack and the second gate structure has asecond gate stack and second gate spacers disposed along sidewalls ofthe second gate stack; a gate via and a gate hard mask, wherein the gatevia is disposed on the first gate stack and between the first gatespacers and the gate hard mask is disposed on the second gate stack andbetween the second gate spacers; and a tri-layer interlayer dielectric(ILD) layer disposed between one of the first gate spacers of the firstgate structure and one of the second gate spacers of the second gatestructure, wherein the tri-layer ILD layer includes: a first dielectriclayer, a second dielectric layer disposed over the first dielectriclayer, a third dielectric layer disposed over the second dielectriclayer, wherein a portion of the third dielectric layer is disposedbetween the gate via and the gate hard mask, and wherein a material ofthe third dielectric layer is different than a material of the gate hardmask and a material of the second dielectric layer.
 20. Thesemiconductor device of claim 19, wherein the third dielectric layer,the second dielectric layer, or both have a void therein.